The present invention relates to a magnetic disc apparatus, and in particular, to a magnetic disc apparatus incorporating a low lift-up slider which can reduce the pressure dependency of the degree of lift-up at the outflow end of the slider.
Japanese Laid-Open Patent No. H5-28682A discloses a conventional magnetic disc apparatus incorporating a head slider having a load fulcrum which is shifted toward the inflow side of the slider in the air-flow direction thereof in order to reduce variation in the degree of the lift-up at the outflow end thereof, which is caused by production unevenness of the head slider, external force during operation, external force given by an air stream or the like, and means for applying a moment around the load fulcrum in order to correct load distribution for a variation which is caused by the shift of the load fulcrum.
In the prior art, since a variation in the load distribution over the slider is compensated for so as to prevent the load from being biased in the air-flow direction of the slider, occurrence of the so-called forward pitching which causes the leading edge, in the air-flow direction, of the slider to continuously rub a magnetic disc, can be restrained even during operation of contact start and stop (which will be hereinbelow simply denoted as (xe2x80x9cCCSxe2x80x9d) even in a conventional start and stop system for the apparatus, thereby it is possible to prevent the slider or the magnetic disc from being damaged by the forward pitching. However, in this arrangement, the resultant force which is composed, perpendicular to the surface of the magnetic disc, of a load and a moment that are exerted to the slider from a suspension acts upon a position in the vicinity of the center point of the slider in the air-flow direction thereof due to the above-mentioned correction for the load distribution, it is required that the resultant force of the aerodynamic forces exerted upon the slider during lift-up acts upon a position in the vicinity of the center point of the slider in the air-flow direction in view of lift-up during lift-up of the slider. That is, in the above-mentioned prior art, it is required to design a shape of a lifting surface of a lifting rail, a lifting pad or the like of the slider in order to allow the resultant force of aerodynamic forces applied to the slider during lift-up thereof to act upon a position in the vicinity of the center point of the slider in the air-flow direction.
With this restrictions, the respective action points of a positive pressure force, that is, a resultant force of positive pressure, a negative pressure force, that is, a resultant force of negative pressure, which are applied to the opposite surfaces of the magnetic disc, and which constitute the resultant forces of the aerodynamic force exerted to the slider, are difficult to optionally set on the opposites surfaces of the slider. Thus, there can be hardly designed the shape of the lifting surface of the slider, which can reduce decrease in the degree of lift-up at the outflow end of the slider due to xe2x80x9clowering of the atmospheric pressure up to an altitude of 3,000 mxe2x80x9d, which mainly causes variation in the degree of lift-up of the outflow end of the slider, and which causes mostly variation in the degree of lift-up at the outflow end of the slider in the conventional apparatus.
The present invention is devised in order to solve the above-mentioned problems inherent to the prior art so as to reduce a decrease in the degree of lift-up at the outflow end of a slider due to the lowering of the atmospheric pressure up to an altitude of 3,000 m which mostly causes variation in the degree of lift-up at the outflow end of the slider in the conventional devices, to a value less than 10 nm or even to zero, and accordingly, an object of the present invention is to provide a non-contact type lift-up slider having a degree of lift-up which is 10 nm or less at the outflow end thereof, and a contact type slider whose contact force is reduced, and is also to provide a magnetic disc apparatus incorporating any of these sliders.
To the end, according to the present invention, there is provided a magnetic disc apparatus comprising a magnetic disc rotatably mounted to a spindle, a slider having an opposed surface opposed to an outer surface of the magnetic disc, one or more than one of lifting surfaces defined by at least one or a combination of those of a lifting rail, a lifting pad, a taper and a step, for producing a positive pressure force which is a resultant force of a positive pressure exerted to the opposed surface, an inflow end which is a frontmost part of the one or more than one of lifting surfaces in a running direction of the slider, an outflow end which is a rearmost part of the one or more than one of lifting surfaces in the running direction of the slider, a slider center point between the inflow end and the outflow end and an overall slider length which is a distance between the inflow end and the outflow end, and also incorporating a magnetic head for recording and reproducing data to and from the magnetic disc, a suspension supporting the slider, for applying a predetermined urging pressure thereto, and a carriage attached to the suspension, for positioning the slider on the magnetic disc, said slider further having an inverted stepped wall formed in such as to be caved from the inflow end to the outflow end of the slider, and a bleed surface formed in the outflow end side of the inverted stepped wall and caved from the lifting rail or the lifting pad, for producing a negative pressure force which is a resultant force of negative pressure exerted to the opposed surface, wherein said suspension is capable of applying a pitching moment which is substantially greater than the product of a value 0.1 times as large as the overall slider length and an urging load, to the slider around the center point, an equivalent load point which is obtained by dividing the pitching moment with the urging load which is offset from the slider center point in the inverted stepped wall of the slider, toward the inflow end on the opposed surface of the slider opposed to the outer surface of the magnetic disc.
Specifically, the above-mentioned equivalent load point is positioned so as to be shifted from an averaged position of the inverted stepped wall of the slider in the overall length direction of the slider, toward the inflow end, and the distance between the equivalent load point and the action point of the above-mentioned positive pressure force is greater than a value about 0.1 times as large as the overall length of the slider.
More specifically, the above-mentioned equivalent load point is positioned so as to be offset from a position which is taken from the inflow end of the slider toward the outflow end thereof by a distance which is about 0.3 times as large as the overall length of the slider, toward the inflow end.